Process for producing practically pure cellulose (alpha-cellulose) from raw cellulose of any origin



Patented. May 22, 1 9,34

PURE CELLULOSE (ALPHA-CELLULOSE) RAW CELLULOSE OF ANY ORIGIN Francesco Carlo Palazzo and Fortunate Palaz 'zo, Florence, Italy No Drawing. Application June 14, 1932, Serial- N0. 617,254. In Switzerland April 22, 1931 6 Claims.

Our present invention has for its object, to provide certain new and improved processes for producing practically pure cellulose (alpha cellulose) from raw celluloses of very different origin and composition, and remove from thelatter the various substances usually accompanying alpha cellulose, by using reactives which, in-the conditions chosen, do not alter in the least the The industrial use of our said,

alpha cellulose. invention, even on the large'stscale, presents no difficulties at all nor requires special apparatuses.

synthetically our said processescomp'rise a plurality-of steps, eachhaving certain features of its own, which succeed each other according to the following diagram:

(1) Boiling in'alkaline solution with sodium hydrate and sodium sulflte,

-(2) Bleaching of product from alkaline boiling with calcium hypochloriteor sodium hyp.o-,

chlorite in a neutral or slightly alkaline solution, or with potassium permanganate in a slightly acid solution, or with all of these systems together, j

(3) Removal of ashes from bleached product eifected with sulfurous' acid or hydrochloric acid,

(4) Forming final product in preferred shapes according to purpose aimed at.

Only in case of having to obtain, for the final product, a particularly high degree of purity we insert between-the second and third steps 1. e. bleaching and ash removal; a fresh but less intense boil ing with -alkaline sodium sulflte solution for sodium hydrate. I

As all of the operative steps,.as said, have their own particular features, we are now going to de-' scribe same particularly, the more so as each of them is liable to modifications within well defined. limits in relation-to origin and composition of the raw cellulose under treatment, and qualities required'for final product.

1. Cooking in alkaline solution are solely determined by the nature (orig-in and composition) of the raw cellulose under treatment, and according to such nature the working pressure mayvary from 0,5 to 2,0 atmosphere, and duration from 1 to 3 hours.

For the other conditions there is, as said, a

certain reciprocal interdependence which leads-- from 40%'-45% of' dry substance) or in suitable presses (containing from 30%-35% of dry substance) or a'still more watery product (withonly 20%-25% of 'dry substance) merely, drained by dripping in tanks with perforated bottom;

the cooking may be started directly after admis- 80 sion of liquor to digester, whilst the procedure will be different in case of a raw cellulose such as immediately'obtained from cooking of a'ligneous material by the bi-sulfite or soda process.

In such case after the usual washings in the 1 digester for removing the greater part of the waste liquor, the alkaline sulfitic liquoris admitted to digester on the already drainedpulp, and circulated by a suitable pump from 5 to 6 times through the whole mass so as to mix same uniformly with the water imbibed by the raw pulp, and thus attain a uniform composition throughoutsaid. mass.

As to raw celluloseswhich-are' already in the shape of boards they are previously reduced to bands by a cutting device, or otherwise subdivided and then placed/in the digester so as to obtain a comparatively compact charge on which the liquor is pumped at such concentration and in such quantity as will be indicated hereafter.

Digesters of various kinds may be used, such as horizontal, vertical or spherical, preferably rotating and permitting, when fixed,'all the same an easy discharge of product and waste liquor. 'After cooking is completed'the digester is discharged down in a tank with perforated bottom where the mass is left to drain for a short time by dIippingQ-Whereafter by repeated sprayings. with water the greater part of the still impregnated waste liquor is expelled. "The pulp thereafter passes to the pulper where it is further washed and reduced to a pulp ready for bleach- In case of the raw cellulose to be treated directly obtained from the-cooking of a ligneous material between the alkaline cooking and bleaching steps a series of mechanical treatments (screening, washing, refining) are inserted, wholly similar to those used for producing ordinary raw cellulose.

(1)) Heating of cligesier Heating of digester is preferably effected by indirect steam, but may also be efifected by direct steam, and in the latter case the original concentration of liquor to be used for cooking is ap propriately modified.

() Concentration of liquor If the raw or starting material consists of raw pulp such as directly obtained from cooking of a lignecus-material, merely washed in the digester, concentration of liquor is to be such as, also considering the ratio of raw cellulose to liquor to be finally a liquor of a tenor of 1% of NaQI-l and 0,5% of NazSCia.

If f. i. between raw cellulose (supposed to be dry) and liquorthere' be'a ratio of 1:10 and the raw pulp only contains of dry substance, for each 100 kg. of dry substance (:500 kg. of wet pulp) 6 hl. of liquor are used, and the latter is to contain a total quantity of 10 kg. of NaOH and 5 kg. of NazsOa so that after mixing the liquor (6111;) with the water imbibed by 100 kg. of dry substance, (4,121.) a liquor will be obtained which corresponds involume to theabove indicated ratio of 1:10, and contains 1% of NaOH and 0,5% of NazSOs.

If, on the other hand, cooking instead of taking place with indirect steam. is efiected by direct steam injected-into the mass, the quantity of condensation water to be produced. in the digester when preparing the liquor must be taken into account, and there-fore one must introduce into the digester a liquor of such concentration that together with the water already. imbibed by the pulp, and with thecondensation water of the direct steam, a liquor is obtained which contains, as above, 1% of NaOH and 0,5% of NaZSOs.

heating a correspondingly higher concentration so as to obtain for the subsequent mixing with the condensation water of direct steam a liquor containing 1,5% of NaOI-I and 0,75% of NazSOz.

(d) Ratiobetween raw cellulose (summed to be dry) and liquor This ratio is liable of some variation according to the condition of the material to be treated.

In case of highly watery material with a tenor water content of 7S% 85%, the said ratio, as in the preceding example, will be 1:10, whilst in case of material which owing to having been squeezed out or centrifugated might have a somewhat lower water content, from to- 55%, a ratio of 1:8 may advantageously be kept, while leaving the concentration of NaHO (1 and that of N21280: (05%) unvaried.

At least, in the particular case of air-dry prodnot with 10%-12% of humidity being used, the

. most convenient ratio to be kept is 1:4, that is to say using 400 litres of liquor for 100 kg. of raw weaves product, which in spite of the higher concentration of the liquor (as prescribed at 0, paragraph 4) implies an economy of reactives as for 100 kg. of air-dry cellulose 6 kg. (instead of 10 kg.)

, of N aOH, and 3 kg. (instead of 5 kg.) of NazSOs are used.

2. Bleaching According to the quality of the product to be bleached, and according to the more or less high degree of bleaching to be aimed at, jointly in any case with a comparative rapidity of the bleaching process, and with a low copper figure (always below 1,0) of finished product, bleaching of product from the alkaline cooking is effected with:

(a) Hypochlorite (of calcium or sodium) in a. slightly alkaline solution,

(b) Potassium permanganate in a slightly acid solution, and

(c) A mixed hypochlorite and permanganatesystem.

(a) The hypochlorite solution containing from 1% to 2% of active chlorine besides a small quantity of calcium hydrate or sodium carbonate, which gives it a slight alkaline reaction, is caused to act at ordinary temperature on the pulp circulating in the pulper at a concentration not above 5%-6%. The bleaching is fairly rapid, and consummation of chlorine referred to 100 kg. of starting raw product does not, usually, exceed kg. 1.

(b) The chameleon solution of 1% of permanganate and 2% of sulphuric acid is also caused to act at ordinary temperature on the pulp circulating in the pulper at a concentration not above 5%6%. The reaction is very rapid, and the consummation of permanganate,-which may be previously estimated by means of an analytical text,-does not usually exceed kg. 1.0 for 100 kg. of starting raw material supposed to be dry.

(c) The pulp at the above indicated concentration of 5%6% is, before all, treated with the hypochlorite solution (at 1%-2% of active chlorine), only :one half of the quantity of chlorine being used which would be necessary .for complete bleaching. When the said quantity of chlorum is entirely absorbed (which only requires a few hours,..even at ordinary temperature) to the said pulpttialways circulating in the pulper, will be added a diluted solution (of 1%) of potassium permanganate slightly acidulated with sulphuric acid (2%) and in such. quantity as to obtain a 3. Removal of ashes from the bleached product In whichever way bleaching may be effected the removal of ashes from bleached product is equally effected with a diluted solution (0,5 %-1 of sulphurous acid acting both on the permanganate and respectively the manganese di-oxyd, and on the small quantity of calcium carbonate or sodium carbonate deposited or, respectively, adsorbed in the 'fibre.

The treatment with sulphurous acid affected in the pulper and not prolonged beyond half an hour is followed by exhaustive washing of pulp, whereafter the product is ultimately subjected to various physical-mechanical treatments according to the shape to be given to final product.

4. Smrmc (a) Flakes and cotton .wool

After centrifugation of pulp in hydro-extractors followed by washing with distilled (condensa-.'

tion) water, the mass is comminuted and reduced to flakes which are ultimately brought to dry condition by carrying them on a suitable apron in counter-current to a hot air current. From the flakes thus obtained a cotton wool is prepared by subjecting them to a special mechanical treatment which, according to the fibres being to be kept long or short, will be effected eitherin a carding machine or in a centrifugal dis-' integrator.

" (1)) Thin. leaves or foils This shape isgiven the pulp in an ordinary continuous machine after previously refining it in the pulper if a product weighing less than 35 gr. for each square meter is to be obtained. The sheet or foil may thenbe wound on reel or variously cut, f.- i. into narrow and short strips,

or in narrow and long ribbons, and so forth;

(c) Felt For preparing the cellulose in the shape of felt the fibre pulp is first treated in a rotary suctionfilter in which the rotation is controlled accordingto the thickness to be given to the felt, and the product fed on an endless apron is dried in counter-movement with an hot air current.

Alkaline cooking of bleached product As said, this cooking is only effected incasecase of wet raw cellulose. 1 As the bleached product after centrifugating or squeezing still contains from 55% to 65% of water, the-liquor is to be of such volume and concentration that-after being put together with the bleached-product, between cellulose (supposed to be air-dried) and liquor there will be a ratio of 1:8, and finally a liquor will be formed containing 1,5% of NaHO and 0,75% 01 NazSOz (or slightly more concentrate if heating be eflfected with direct steam).

or course, if this treamentis .to be applied to the product already bleached, the preceding bleaching may be effected by using a slight excess of oxydant. In this way, in the case of wood cellulose,- the last traces of lignine will be completely removed, whilst the small quantity of oxydellulose which may be formed owing to said excess, does not ultimately go to contaminate the bleached product because it goes into solution in the subsequent alkaline sulfite treatment.

A particular feature of the above described boiling consists in the recovery of the greater part in volume) of the waste liquor, the

product was obtained, and such cooking process quite normally as the liquor besides the two un-' altered reactives NaOH and NazSOa duly contains a very small quantity of organic substance;

As to the centrifugated or squeezed product,

this is treated for a short period in the pulper and finally for the removal of the ashes therefrom, or intheabove said way with sulphurous acid or, in an analogous way with an equivalent quantity of hydrochloric acid.

Having now particularly described and ascer-- tained the nature of our said inven ion-and in what manner the same is to be performed, we declare that what we claimis:

'1. Process for producing, from raw cellulose of any origin, practically pure cellulose with 96% unto 99%,of alpha-cellulose, copper figure from 0.8 to 0.2,ether-soluble substances from 0.15 to 0;05% and ashes from 0.18% to 0.10%, which process consists in cooking said celluloses in the most variated conditions. wet or air-dry, purified or not purified, in a digester with an alkaline-'- s'ulfitic liquor containing from 0.5 to 1.5% of NaOH and'irom 0.25% to 0.75% of NaaSOs. un-

der a pressure from 0.5 to 2 atm.. and for a pe-' riod variable between 1 and 3 hours; the material obtained fromuthe said cooking at a concentration of 5% to 6% being thereupon bleached at ordinary temperature with a diluted potassium permanganate solution of 1%,,acidula'ted with 2% of sulphuric acid.

2. Process for producing, from raw cellulose .ofany origin, practically pure cellulose with 96% up to-99% of alpha-cellulose. copper figure from 0.8 to 0.2. ether-soluble substances from 0.15 to 0.05% and ashes from 0.18% to 0.10%, whichprocess' consists in cooking said celluloses in the most variated conditions, wet or air-dry. Durified or not purified, in a digester with an alkalinesulfitic liquor containing from 0.5 to 1.5% of NaOH and from 0.25% to 0.75% of NaZSOa. un-

der a pressure from 0.5 to 2 atm., and for a period variable between land 3 hours, the product thus obtained being then treated in a digester with an alkaline-sulfitic liquor at a pressure of 3.'Process' as claimed in claim 2, characterized in that the final product obtained from said chemical treatments is furthermore subjected to suitable physical-mechanical treatmentsso as to form the same at will in the shape of flakes} cottonwool. thin'sheets or leaves, reels, bands, ribbons or felt. h

4'; Process forproducing, from raw cellulose of any origin, practically pure cellulose with 96% up to 99% of'alpha-cellulose, copper figure from 0.8 to 0.2, ether-soluble substances from 0.15 to 0.05% and ashes from 0.18% to 0.10%.which process consists in cooking said celluloses in the most variated conditions, wet or air-dry, purified or not purified, ina digester with an alkalinesulfitic liquor containing from 0.5 to 1.5% of NaOH and from 0.25% to 0.75% of NazSOa, under a pressure from 0.5 to 2 atm., and for a period variable between 1 and 3 hours: the material obtained from cookin in a'concentration of 5 to 6% thereupon being bleached at ordinary temperature with a diluted solutionot calcium or sodium hypochlorite, containing 1 to 2% of effective chlorine besides a small quantity of calcium hydrate or, respectively, sodium carbonate and, after washing, again treated at ordinary temperature with a diluted solution at 0.5 to 1% of sulphurous acid, whereupon an exhaustive washing in the pulper is efifected.

5. Process for producing, from raw cellulose of any origin, practically pure cellulose with 96% up to 99% of alpha-cellulose, copper figure from 0.0 to 0.2, ether-soluble substances from 0.15 to 0.05% and ashes from 0.18% to 0.10%, which process consists in cooking said celluloses in the most variated conditions, wet or air-dry, purified or not purified, in a digester with an alkaline suliitic liquor containing from 0.5 to 1.5% of NaOH and from 0.25% to 0.75% of NaaSOa, ,under a pressure from 0.5 to 2 atm., and for a period variable between 1 and 3 hours; the material obtained from cooking in a concentration of 5 to 6% thereupon being partially bleached at ordinary temperature with a diluted solution of hypolution, at 1%, of potassium permanganate, acidulated with sulfuric acid of 2% strength.

6. Process for producing, from raw cellulose of any origin, practically pure cellulose with 96% up to 99% of alpha-cellulose, copper figure from 0.8 to 0.2, ether-soluble substancesfrom 0.15 to 0.05% and ashes from 0.18% to 0.10%, which process consists in cooking said celluloses in the most variated conditions, wet or air-dry, purified or not purified, in a digester with an alkalinesulfitic liquor containing from 0.5 to 1.5% of NaOH and from 0.25% to 0.75% of NazSOa, under a pressure from 0.5 to 2 atm., and for a period variable between 1 and 3 hours; the material obtained from cooking in a concentration of 5 to 6% being first bleached and then, after washing, treated in autoclave with an alkalisulfitic liquor at a pressure of 0.5 to 1.0 atmosphere for a period of 1 hour, washed again, and finally treated with a diluted solution at 0.5 to 1% of sulphurous acid or another equivalent solution of hydrochloric acid, and exhaustive Washing in pulper.

FRANCESCO CARLO PALAZZO. FORI'UNATO PALAZZO. 

